A generation of a plasma by a gaseous phase discharge has been widely used for synthesis of various kinds of substances such as synthesis of a thin film on a solid phase surface and the like. Species, which bring about a gaseous phase reaction, such as electrons, ions and various kinds of excited species, that is activated species, are produced in a plasma generated by said gaseous phase discharge to make said gaseous phase reaction progress.
A representative practical example of said activated species-generating apparatus using a discharge includes an ozonizer synthesizing ozone and also a removal of harmful substances (nitrogen oxides and the like) and the like by said discharge generate said activated species similarly to utilize reactions brought about by the activated species.
In such activated species-generating apparatus, it is important how efficiently electrons are brought into collision with molecules in a gaseous please during the gaseous phase discharge, that is, how efficiently electron energies are utilized for turning said molecules into the activated species during said collision. Consequently, has been well known that in said practical ozonizer a metal-metal discharge is not carried out but a dielectric layer is disposed between metals to disperse the discharge in a space, micronizing the discharge.
in addition, in order to control said electron energies generated, also an activated species-generating apparatus, in which metallic wires are crowded in for example a netted shape to form an electrode, has been disclosed in Japanese Patent Publication No. Sho 61-32242. A typical construction of this apparatus in the case where it is used as the ozonizer is shown in FIG. 10.
A three-dimensionally crowded electrode 92, in which metallic wires are entangledly crowded, is inserted into the side of an inner surface of a cylindrical dielectric 91. A surface electrode 93 formed of a metallic layer is clad as an electrode forming a counterpart to said crowded electrode 92 on a circumferential surface of said dielectric 91. And, a material gas, such as air and oxygen, is passed through an inside of the dielectric 91 and a voltage is applied between the crowded electrode 92 and said surface electrode 93 through a power-supplying rod 94 inserted into an axis shaft line portion within the dielectric 91 to generate a corona discharge between the dielectric 91 and the crowded electrode 92, thereby ozonizing said material gas (refer to OZONE SCIENCE & ENGINEERING., 10, pp. 137-151).
Such activated species-generating apparatus is characterized in that a starting voltage of said corona discharge can be controlled over a wide range by regulating a diameter, bulk density and the like of wires in the crowded electrode. As a result, in the ozonizer, a remarkably high ozone-generating efficiency can be obtained within a low discharge voltage range close to a discharge-starting voltage. Furthermore, since a sectional shape of a gaseous flow can be freely set, a pressure loss for said gaseous flow is remarkably reduced as compared with that in a discharge space in which a dielectric is disposed between a flat plate-type electrode and a cylinder-type electrode in a usual ozonizer. Besides, it: has been confirmed that the above described activated species-generating apparatus also exhibits the same effects as in the usual ozonizer also in other respects.
However, on the other hand, a disadvantage occurs in that a discharge range is limited by a two-dimensional range along a surface of the dielectric. Accordingly, it, is difficult to say that a gain of the crowded electrode consisting of a three-dimensional mass of metallic wires is sufficiently utilized.
It is an object of the present invention to provide a highly efficient clad fine wire electrode-type activated species-generating apparatus in which a discharge range is not limited by a flat and narrow range brought into contact with a dielectric but developed all over the range where fine wires exist.